Today, millions of people are living with cancer or have had cancer. To provide effective treatments for a particular type of cancer, cancers should be classified according to their molecular characteristics. The molecular characteristics of individual tumors can be used to tailor treatment regimens, monitor the response to treatment, and to detect residual diseases. The major goal of this proposal is to develop a panel of aptamers as novel molecular probes for molecular profiling of leukemia cells. The biggest advantage of the aptamer- based technology is the unique cell-based selection process, Cell- SELEX (Systematic Evolution of Ligands by Exponential enrichment), used in the proposed studies. A group of cell-specific aptamers can be selected using a subtraction strategy in a relatively short period without even knowing which target molecules are present on the cell surface. Once specific aptamers are selected, we can begin to profile tumor cells without identifying each individual target proteins. These types of studies cannot be done with other types of technologies used for proteonomic studies. Also, not only can the selected aptamers be used as molecular probes for molecular profiling, but they can be used as tools for identifying new biomarkers expressed by tumor cells or other cells in disease status. The stability and easy synthesis of DNA-aptamer probes will have many more advantages than antibodies in making microarrays for proteonomic molecular profiling. Thus, aptamer technology holds a promise to overcome the challenges in current molecular profiling of normal or tumor cells. We begin our studies with well-characterized leukemia cell lines to develop the cell-based SELEX methodologies. We are then going to use patients' leukemia specimens or tumor tissue sections to select aptamers that can recognize patients' leukemia cells or formalin-fixed tumor cells. The developed strategies using leukemia cell lines or lymphoma tumor sections should easily be applied to other cancer cell lines or clinical specimens. By the completion of this project, we will have produced panels of aptamer probes for different types of leukemias. With flow cytometry or tools of imaging analysis, the cell-specific aptamers are valuable probes for molecular diagnosis and classification of tumors, as well as for the evaluation of the effects of drugs on cancer cells, which in turn will improve the diagnosis and therapy of cancers. This project is to use cell-based SELEX methodologies for developing novel DNA aptamer probes that can recognize patients' leukemia or lymphoma cells. The cell-specific aptamers are valuable probes for molecular diagnosis and classification of tumors, as well as for the evaluation of the effects of drugs on cancer cells, which in turn will improve the diagnosis and therapy of cancers.